Mammography is an x-ray examination of the female breast carried out using medical imaging apparatuses for obtaining mammographic images. Such apparatuses usually have an x-ray radiation source. The female breast under examination is exposed to x-ray radiation in order to obtain a projection x-ray image on an x-ray film disposed in the beam path beneath said female breast. During the examination the female breast is usually held between two compression plates.
The advantage of using x-ray films is that they provide a relatively sophisticated and, at least in terms of outlay, relatively inexpensive solution, while at the same time allowing long-term archiving of an acquired projection x-ray image using this medium.
Another advantage of using x-ray films is that x-ray films have a very large receiving area of typically 18×24 cm or 24×30 cm and a relatively high local resolution of approximately 14 LP/mm (LP=linear pairs), making it possible to create a high-resolution complete recording of the female breast in a single test.
The disadvantage of using x-ray films is that the images are not available in real-time, as the film must first be developed.
Instead of x-ray film, which can be used only once, a known solution is to use charge-coupled-device (CCD) sensors which can replace the x-ray film in a mammography machine.
In order to facilitate conversion of the equipment, the CCD sensors often have the same shape as conventional x-ray film cassettes. Such CCD sensors can be easily inserted in an existing mount for x-ray film cassettes. CCD sensors are electronic components suitable for locally resolving radiation measurement, in particular x-ray radiation, and generally consist of an array of radiation-sensitive cells also known as pixels.
The advantage of using CCD sensors is that, on the one hand, modern CCD sensors have a resolution of 10-20 LP/mm which in some cases exceeds the resolution of x-ray films and that, on the other hand, the images can be immediately made available and digitally processed. Unlike x-ray films, CCD sensors are therefore suitable for obtaining real-time images (during a biopsy, for example).
The disadvantage of using CCD sensors is that known CCD sensors with the required high resolution have a receiving surface which is much smaller than the receiving surface of x-ray films. Therefore, high-resolution CCD sensors are currently only suitable for capturing detailed images of the female breast or for stereotactical biopsy.
Additionally, known in the context of FFDM (Full Field Digital Mammography) is the use of low-resolution digital detectors.
Although the digital detectors used for FFDM have a resolution of typically 5 to 10 LP per millimeter and therefore a lower resolution than x-ray films, receiving surfaces having a size similar to the size of the receiving surfaces of conventional x-ray films can be implemented. Using the FFDM detectors, it is therefore possible to create a complete image of the female breast with a single test.
Advantages of FFDM detectors are therefore that the images are available in real-time, can be digitally processed, and the receiving surfaces are relatively large. The disadvantage is the relatively low resolution.
As an alternative to high- or low-resolution CCD sensors for obtaining mammographic images, the use of digital luminescence radiography with storage foil technology is also known.
In order to be able to make a reliable diagnosis as to whether a lump discovered in the female breast during mammography is benign or malignant, the creation of mammographic images is generally insufficient. Rather, it is usually necessary to extract a tissue sample from the breast as part of a biopsy, the lump in question first being located using a medical imaging apparatus for obtaining mammographic images and a biopsy needle for removing a tissue sample being inserted in the breast with a manipulator attached to the apparatus. When using a digital sensor for the x-ray radiation, this takes place under continuous monitoring by the medical imaging apparatus. Using an FFDM sensor for this purpose is generally insufficient, as the resolution is too low to ensure that the biopsy needle has actually reached the suspicious lump. Such continuous monitoring by the medical imaging apparatus is not possible when using an x-ray film.
In order to be able to combine the advantages of, for example, an FFDM sensor with the advantage of x-ray film or of a high-resolution CCD sensor, medical imaging apparatuses for obtaining mammographic images are known which have two receiving surfaces for x-ray radiation. The manipulator is mounted on such an apparatus in some cases by a separate support independent of the receiving surfaces. In other cases the manipulator is disposed directly on a receiving surface.
A related art apparatus with two receiving surfaces and manipulator will now be described in greater detail with reference to FIG. 4. The apparatus 41 for obtaining mammographic images has a head 42 with a radiation source 43 for emitting x-ray radiation 44 and a receiving device support 45. Both the head 42 and the receiving device support 45 are supported by a supporting column 46 via a mount 54. The supporting column 46 can be free-standing or fixed to the floor or ceiling of a room.
The receiving device support 45 has a first receiving surface 48 in the form of a holder for x-ray films and a second receiving surface 49 in the form of a large-area low-resolution detector with approx. 5-10 LP/mm for FFDM images.
The x-ray film holder is designed such that it can also accommodate a high-resolution CCD sensor. The high-resolution CCD sensor can then be connected to a suitable processing device or to the apparatus 41 by a connecting line (not shown). CCD sensors of this kind currently only have a receiving surface area of approximately 50 mm×80 mm and are incorporated in a mount having the same dimensions as an x-ray film cassette.
The two receiving surfaces 48 and 49 mounted to the receiving device support 45 are disposed at right angles to one another and are supported by the mount 54. The two receiving surfaces 48 and 49 can be alternately rotated about an axis of rotation 50 to a test position with a motor in the receiving device support 45. The axis of rotation 50 makes an angle of about 45° with the beam path of the x-ray radiation 44 emitted by the x-ray source 43. Such a design of the mounting of the receiving surfaces is known as “flying wing”.
The angle of about 45° between the axis of rotation 50 and beam path of the x-ray radiation 44 ensures, in conjunction with the receiving surfaces 48, 49 disposed at an angle of 90° to one another, that by swiveling the support 45 about the axis of rotation 50, one of the receiving surfaces 48 outside the beam path can be disposed essentially parallel to the beam path and the other receiving surface 49 inside the beam path can be disposed essentially perpendicular to the beam path of the x-ray radiation 44.
In the beam path between a receiving surface 48 or 49 in the test position and the radiation source 43, a test area for disposing a test object 47 (for example, a female breast) is provided.
A biopsy unit 52 is supported by the receiving surface 49 disposed inside the beam path substantially perpendicular to the beam path of the x-ray radiation 44.
The biopsy unit 52 is suitable for taking tissue samples from the female breast 47 and supports a compression plate 53.
Alternatively, however, it is possible for the compression plate 53 to be supported and moved not by the biopsy unit 52 but by a compression device 51 of the medical imaging apparatus 41. In this case, the element 53 is a device for positioning and guiding a biopsy needle.
In addition, currently known biopsy units often incorporate a stage (not shown in FIG. 4) into which a film cassette or CCD sensor can be inserted.
By vertical movement of the compression plate 53 by the biopsy unit 52 or the compression device 51, it is possible to compress and hold the female breast 47 in the test area between the compression plate 53 and the receiving surface 48 or 49 in the test position.
As the compression plate 53 is disposed in the beam path of the x-ray radiation, it is a radiation-transparent material.
The disadvantage of the known apparatus is that, due to the projecting swiveling motion of the receiving surfaces 48 and 49, it has a high space requirement. In addition, manufacturing a correspondingly rotatable mechanical connection to the relevant receiving surfaces 48, 49 with the precision required in medical engineering is very demanding technically and therefore expensive.
Another disadvantage of the known design is that the head 42 incorporating the radiation source 43 and the receiving device support 45 are supported by a common mount 54. This complicates the design of the apparatus shown in FIG. 4, as the head 42 with the radiation source 43 must be electronically and mechanically decoupled from the rotary motion of the receiving device support 45. A further disadvantage is that an electrical connection to the second receiving surface 49 is generally provided with a separate cable which obstructs the swiveling motion of the receiving device support 45 and can easily be accidentally loosened.